An Analysis of Unicellular Mass Transfer Using a Microfabricated Experimental Technique

Using microfabrication technology, we have developed a new experimental apparatus and technique which allow isolation of individual cells and which facilitate the study of kinetic volume changes and membrane permeability. The key component of the apparatus is a microdiffusion chamber which was constructed using silicon microfabrication technology and standard photolithography. The central unit of the chamber is a 1 \mubm thick silicon nitride membrane with a center hole on the order of 2-3 \mubm in diameter. The device is novel in its analysis of a single cell, instead of the traditional array of cells, and its avoidance of the damage artifacts and computational difficulties which are inherent in other, commonly used methods of cellular analysis. The device is used in conjunction with a predictive computer model which simulates the response of the entire membrane or a portion of the membrane to various permeant and impermeant concentrations. This study introduces the apparatus and the model, and illustrates the effectiveness of the new procedure by determining several membrane permeability coefficients for HBL-100 (healthy human breast line). The empirical data and theoretical data were combined to yield a water permability \bi(L_{p}) of \bf 1.1\,\bpm\, 0.5\,\mub\hbox{m/(min-atm)} (mean \bpm 1 standard deviation) (\bi N=5) during the uncoupled transport of water at 22 [degrees]C. In the presence of 6 M glycerol, the water permeability \bi(L_{p}), permeability coefficient \bi (P_{S}), and the reflection coefficient \bi(\sigmab_{S}) were determined to be \bf 2.0\,\bpm\, 0.63\,\mu\hbox{m/(min-atm)}, 2.7E-5 \bpm 6.1E-6 {\bf cm-sec}^{-1}, and \bf0.76\,\bpm\, 0.5 ({\bi N}=6). No previous values of these coefficients could be found for HBL-100 cells.